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An investigation of the parameters governing both the binding of small molecules to different tungsten complexes and agostic bonding in the W[(CO).sub.3][(P[Cy.sub.3]).sub.2] complex applying ab initio MP2 calculations with and without basis set superposition error (BSSE) correction is described. It is suggested that BSSE correction are a must for quantitative predictions for bimolecular reactions.

The binding of a dihydrogen molecule ([H.sub.2]) to a transition metal center in an organometallic complex was a major discovery because it changed the way chemists think about the reactivity of molecules with chemically 'inert' strong bonds such as H-H and C-H. Before the seminal finding of side-on bonded [H.sub.2] in W[(CO).sub.3][(P[R.sub.3]).sub.2]([H.sub.2]), it was generally believed that [H.sub.2] could not bind to another atom in stable fashion and would split into two separate H atoms to form a metal dihydride before undergoing chemical reaction. Metal-bound saturated molecules such as [H.sub.2], silanes, and alkanes ([sigma]-complexes) have a chemistry of their own, with surprisingly varied structures, bonding, and dynamics. [H.sub.2] complexes are of increased relevance for [H.sub.2] production and storage in the hydrogen economy of the future.

The synthesis and characterization of cationic platinum complexes of the type [(R (sub 2) PC (sub 2) H (sub 4) PR (sub 2)) PtMe (OEt (sub 2))] BAr (sub F) (R =Cy, Et) are reported. A possible mechanism is proposed for the C-C coupling reaction based upon the structures of these bridging biphenyl complexes, which provides a new perspective for the related palladium-catalyzed oxidative coupling of arenes to form analysis.

The chemistry of the binding and reactivity of dihydrogen ([H.sub.2]) on different transition metals underlying the hydrogenase function and the production and storage of [H.sub.2] is described. These new storage methods can be easily used, as the [H.sub.2] molecules can easily bind with various materials.

The structural, thermochemical and kinetic studies of a mechanism of formation of [[Mo([mu].TeAr)[(CO).sub.3](Pi[P.sub.3])].sub.2] by phosphine elimination from [super .]Mo(TePh)[(CO).sub.3][(Pi[Pr.sub.3]).sub.2] are reported. The rate of reaction of ([super .]TeAr)W-[(CO).sub.3][(Pi[Pr.sub.3]).sub.2] and CO is found to be first-order in the metal complex and is proposed to proceed by the associative formation of the 19 [e.sup.-] radical complex ([super .]TePh)W-[(CO).sub.4][(Pi[Pr.sub.3]).sub.2], which extrudes a [super .]TePh radical.

The reactivity of the phenyl dichalcogenides (PhE-EPh, E = S, Se, Te) with three metal complexes M[(CO).sub.3][(P[R.sub.3]).sub.2], W(CO)3(PR3)2 and Mo[(N[[t.sub.Bu]]Ar).sub.3] is investigated. The calculations of electron densities of the SOMO have shown the increasing electron density on the chalcogen atom on going from S to Se to Te.

A new series of Fe(II), FeCl2{N(R)=C(Me)=N(R)} containing diimine ligands with hemiliable sidearms R (R=CH2(CH2)2NMe(sub 2), CH2(CH2)2OMe, CH2(CH2)2SMe) were synthesized. It was found that interaction of Co with high-spin 5-coordinate Fe model complex is thermoneutral but favored to low-spin diphosphine fragments.

Abstract: Fifty years ago, when this journal was founded, organometallic chemists could not have imagined that common small molecules such as dinitrogen and especially dihydrogen could function as ligands. Dihydrogen has long been vital in catalytic processes such as hydrogenation and conversions of organic compounds and is now being considered as a future energy storage medium. Dihydrogen is only useful chemically when the two strongly bound H atoms are split apart in a controlled fashion. Although metal hydrides were first well established in 1955, the structure and mechanism by which H2 binds to and undergoes cleavage on transition metals was not ascertained until even more recently in the history of inorganometallic chemistry, about 20 years after this journal was first published. The activation of dihydrogen is a fascinating saga that has slowly unfolded over the past 80+ years, as will be chronicled in this Perspective. There is a marvelous analogy between the metal-olefin π bonding model first brought to light by Dewar, Chatt, and Duncanson 60 years ago and the bonding model for side-on σ-bond coordination discovered by us 30 years ago. There are two separate pathways for H–H (and X–H σ-bond activation in general) that directly depend on the electronics of the metal σ-ligand bonding. Metal d to σ* X–H backdonation is the key to stabilizing σ-bond coordination and also is crucial to its homolytic cleavage (oxidation addition). For electrophilic complexes, particularly cationic systems with minimal backdonation, heterolytic cleavage of H2 is common and is a key reaction in industrial and biological catalysis. [Copyright &y& Elsevier]

Abstract: This perspective article serves to highlight the contributions to this special volume of Journal of Organometallic Chemistry entitled “Organometallics for Energy Conversion”. The key features of dihydrogen coordination to transition metal complexes are discussed in the context of the challenge of producing and utilizing hydrogen as the energy carrier of the future. Ultimately, production of H2 fuel from water will be needed rather than its current production principally from natural gas. Schemes involving use of solar energy to split water are currently of high interest, and a massive research effort is underway worldwide to accomplish this goal. This is primarily a chemistry problem (rather than engineering or materials), and it can then be assumed that organometallic chemistry will play an important role for both hydrogen production and storage. [Copyright &y& Elsevier]

The article reports on the principles of dihydrogen (H2) binding and reactivity on transition metals implicit in hydrogenase function and H2 production and storage. It focuses on the occurrence of H2 activation on metal complexes and on enzymes including hydrogenases. The author highlights the need for further research on the ability of H2 molecules to bind to a diversity of materials toward the discovery of new hydrogen storage methods.

The crystal structure of the first homoleptic manganese-phosphine complex, [Mn(Me2 PC2H4PMe2)3][BF4], has been determined. This complex, previously synthesized as a PF6 salt characterized only by NMR spectroscopy, is a by-product of reaction of MnH3(Me2PC2H4PMe2)2 with [Ag(CH3CN)4] [BF4]. It crystallizes in the trigonal system, space group P31c and Z = 2. The structure shows 3 chelating diphosphine ligands coordinating to the central manganese cation in octahedral fashion. The Mn-P distances are essentially equivalent within 3σ: each diphosphine has Mn-P = 2.283(3) and 2.290(3) Å, where the "short" and "long" distances are trans to each other. The "bite angle" for each diphosphine is 83.57(9)°, Lattice parameters: a = 9.954(2) Å, b = 9.954(2) Å, c = 16.416(2) Å. Unit cell volume: 1408.6(4) ų. [ABSTRACT FROM AUTHOR]

Studies the equilibrium isotope effect on dihydrogen (H2) binding in a M(...2-H2) complex. Normal coordinate analysis; Calculation of the equilibrium isotope effect for the reversible binding of H2 and dideuterium; Comparison of the equilibrium constants.

Studies the coordination of the hydrogen atom in the molybdenum complex, Mo(CO)(H2)[(C6D5)2PC2H4P(C6D5)2]2.4.5C6D6. Implications on the reaction coordinate for hydrogen-hydrogen cleavage to dihydride; Electronic considerations; Measurement of the barrier to rotation of the hydrogen atom; Indications of librational motion; Extension of Huckel calculations; More.

Reports the synthesis and characterization of the bridging dinitrogen complex {Mo(CO)-(Et2PC2H4PEt2)2}2(mu-N2) and the two agostic complexes Mo(CO)(R2PC2H4PR2)2(R=Et(2), Bui(3)). Synthesis and spectroscopic characterization of the bridging dinitrogen complex; X-ray crystal structure; Procedures for synthesis; X-ray crystallographic analysis.

Discusses the synthesis and characterization of molybdenum complexes containing diphosphine ligands. Electronic control of nu2-dihydrogen versus dihydride coordination; Implications on the reaction coordinate for hydrogen cleavage.

Examines first-row members of the group 6 series of transition metal dihydrogen complexes Cr(CO)3(PR3)2(eta2-H2)(R=Cy, Pri). Solution and solid state nuclear magnetic resonance (NMR) studies; Comparison of H-H distances determined by diffraction and solid state NMR methods; Vibrational and rotational dynamics of Cr(CO)3(PCy3)2(H2).

The article focuses on the breaking of molecular hydrogen and its reunion. Molecular hydrogen is not only a future fuel, it is widely used in chemical reactions. The adding of molecular hydrogen to organic compounds is known as hydrogenation, it is among the largest used human-made chemical reaction. Catalytic hydrogenation is widely used in various industries. It is possible to split molecular hydrogen in a controlled manner on metal catalysts and a few nonmetal compounds, but the process of reunion of hydrogen bond is difficult and has never been accomplished on a nonmetal compound. But a new discovery has made possible the reversible nature of the hydrogen activation.

Describes the first examples of transition metal eta2-SiH4 complexes and an unprecedented tautomeric equilibrium between an eta2-SiH4 complex and a hydridosilyl species. Agostic interaction in Mo(CO)(R2PC2H4PR2)2; Confirmation of eta2-coordination; Nuclear magnetic resonance (NMR) data and crystal structure.

The complexes (•TeAr)Mo(CO)3(PiPr3)2 (Ar = phenyl, naphthyl; iPr = isopropyl) slowly eliminate PiPr3 at room temperature in a toluene solution to quantitatively form the dinuclear complexes [Mo(μ-TeAr)(CO)3(PiPr3)]2. The crystal structure of [Mo(μ-Te-naphthyl)(CO)3(PiPr3)]2 is reported and has a Mo-Mo distance of 3.2130 Å. The enthalpy of dimerization has been measured and is used to estimate a Mo-Mo bond strength on the order of 30 kcal mol-1. Kinetic studies show the rate of formation of the dimeric chalcogen bridged complex is best fit by a rate law first order in (•TeAr)Mo(CO)3(PiPr3)2 and inhibited by added PPr3. The reaction is proposed to occur by initial dissociation of a phosphine ligand and not by radical recombination of 2 mol of (•TeAr)Mo(CO)3(PiPr3)2. Reaction of (•TePh)Mo(CO)3(PiPr3)2, with L = pyridine (py) or CO, is rapid and quantitative at room temperature to form PhTeTePh and Mo(L)(CO)3(PiPr3)2, in keeping with thermochemical predictions. The rate of reaction of (•TeAr)W-(CO)3(PiPr3)2 and CO is first-order in the metal complex and is proposed to proceed by the associative formation of the 19 e- radical complex (•TePh)W(CO)4(PiPr3)2 which extrudes a •TePh radical. [ABSTRACT FROM AUTHOR]

Enthalpies of oxidative addition of PhE–EPh (E = S, Se, Te) to the M(0) complexes M(PiPr3)2- (CO)3 (M = Mo, W) to form stable complexes M(*EPh)(PiPr3)2(CO)3 are reported and compared to analogous data for addition to the Mo(III) complexes Mo(N[tBu]Ar)3 (Ar = 3,5-C6H3Me2) to form diamagnetic Mo(IV) phenyl chalcogenide complexes Mo(N[tu]Ar)3(EPh). Reactions are increasingly exothermic based on metal complex, Mo(PiPr3)2(CO)3 < W(PiPr3)2(CO)3 < Mo(N[tBu]Ar)3, and in terms of chalcogenide, PhTe–TePh < PhSe–SePh < PhS–SPh. These data are used to calculate LnM–EPh bond strengths, which are used to estimate the energetics of production of a free *EPh radical when a dichalcogenide interacts with a specific metal complex. To test these data, reactions of Mo(N[tBu]Ar)3 and Mo(PiPr3)2(CO)3 with PhSe–SePh were studied by stopped-flow kinetics. First- and second-order dependence on metal ion concentration was determined for these two complexes, respectively, in keeping with predictions based on thermochemical data. ESR data are reported for the full set of bound chalcogenyl radical complexes (PhE*)M(PiPr3)2(CO)3; g values increase on going from S to Se, to Te, and from Mo to W. Calculations of electron densities of the SOMO show increasing electron density on the chalcogen atom on going from S to Se to Te. The crystal structure of W(*TePh)(PiPr3)2(CO)3 is reported. [ABSTRACT FROM AUTHOR]

Reactions of W(CO)3(phen)(EtCN) with butane thiols, thiophenol, 1,2-benzenedithiol, and 3,4-toluenedithiol have been investigated. Reaction of butanethiol results in simple ligand exchange to form the thiol complex W(CO)3(phen)(n or tBuSH). Reaction with thiophenol results in oxidative addition to form the W(II) thiolate hydride complex W (CO)3(phen)(SPh)(H). The lower reducing power of Mo compared to W is demonstrated in that simple ligand binding of PhSH to Mo(0) occurs forming Mo(CO)3(phen)(PhSH). Reactions of arene dithiols with W(CO)3(phen)(EtCN) were found to proceed with initial oxidative addition of one S–H bond of the chelating dithiols to form W(CO)3(phen)(H)[S–arene(SH)]. These complexes slowly eliminate H2 and CO to form W(CO)2(phen)(arenedithiolate) complexes. The same complexes can be formed by thiol/thiolate exchange reactions: W(CO)2(phen)(SR)2 (R=tBu, Ph) react quantitatively with arene dithiol to yield W(CO)2(phen)(arenedithiolate). The crystal structure of W(CO)2(phen)(3,4-toluenedithiolate) has been determined and is trigonal prismatic rather than octahedral. Values for ΔH° (thiol/thiolate exchange) have been measured by solution calorimetry relative to W(CO)2(phen)(StBu)2=0.0 kcal mol−1; (CO)2(phen)(SPh)2=−7.2±0.4 kcal mol−1 and W(CO)2(phen)(3,4-toluenedithiolate)=−12.5±0.6 kcal mol−1. [Copyright &y& Elsevier]

Discusses the results of the international workshop on carbon management organized under the auspices of the United States Department of Energy Council on Chemical Sciences in Santa Fe, New Mexico held from April 30 to May 4, 1999. Hydrogen generation and carbon management; Selective functionalization of hydrocarbons; Utilization of carbon dioxide; Catalysis related to efficient engines for transportation.

Proposes a unified description of the effects of the coherent and incoherent dihydrogen exchange on the NMR and INS spectra of transition metal hydrides. What the effects of the transition metal hydrides are based on; Description of experiments conducted in the study; Illustration of coherent versus incoherent dihydrogene exchange in transition metal hydrides; Discussion on the results of the study.

The complexes (*TeAr)Mo(CO)3(PiPr3)2 (Ar = phenyl, naphthyl; iPr = isopropyl) slowly eliminate PiPr3 at room temperature in a toluene solution to quantitatively form the dinuclear complexes [Mo(mu-TeAr)(CO)3(PiPr3)]2. The crystal structure of [Mo(mu-Te-naphthyl)(CO)3(PiPr3)]2 is reported and has a Mo-Mo distance of 3.2130 A. The enthalpy of dimerization has been measured and is used to estimate a Mo-Mo bond strength on the order of 30 kcal mol-1. Kinetic studies show the rate of formation of the dimeric chalcogen bridged complex is best fit by a rate law first order in (*TeAr)Mo(CO)3(PiPr3)2 and inhibited by added PiPr3. The reaction is proposed to occur by initial dissociation of a phosphine ligand and not by radical recombination of 2 mol of (*TeAr)Mo(CO)3(PiPr3)2. Reaction of (*TePh)Mo(CO)3(PiPr3)2, with L = pyridine (py) or CO, is rapid and quantitative at room temperature to form PhTeTePh and Mo(L)(CO)3(PiPr3)2, in keeping with thermochemical predictions. The rate of reaction of (*TeAr)W(CO)3(PiPr3)2 and CO is first-order in the metal complex and is proposed to proceed by the associative formation of the 19 e- radical complex (*TePh)W(CO)4(PiPr3)2 which extrudes a *TePh radical.